This invention relates generally to a means for maintaining preloads on a bearing supporting a rotatable shaft and, more particularly, to a retainer which cooperates with a conventional lock nut maintaining the preload so as to prevent rotation of the lock nut relative to the shaft.
While this invention may be employed in many fields, it is particularly useful in confunction with drive assemblies for heavy-duty earthmoving equipment, such as crawler tractors and the like. The final drive and the traction chains located on each side of the crawler tractor are subjected to substantial radial and axial thrust loads. These loads are the result of the high driving force required for operation and the erratic loading placed on the tractor drive because of rough terrain, side hill operation and directional changes.
In order to provide sufficient friction free support for the highly-loaded rotatable drive shafts, shock resistant, heavy-duty, tapered roller bearings are employed. If properly arranged and preloaded, these tapered roller bearings have inherent capability to efficiently accommodate both radial and axial thrust loads. In order to withstand high stress loads and deflection of components, it is vital that the required preloads on the tapered roller bearings be maintained so as to provide rigidity, positive support and extended service life for the bearings and the associated components.
In the prior art, it is a common practice to plate a lock nut onto the rotating shaft to bear against the bearing in an attempt to maintain prescribed bearing preloads. However, a conventional lock nut has a tendency to work loose during operation so that the bearing preload is diminished. In general, rotation of the lock nut ten degrees will alter the breakaway torque of the lock nut by approximately 100 foot-pounds.
It is possible to make periodic inspections and service adjustments of the bearing and the lock nut. In some applications, ready accessibility makes these inspections and adjustments expedient. Even when the bearings and the lock nuts are not readily accessible, prudent inspections and periodic service should not be ignored. In the case of crawler tractors where the track chains and the drive sprockets must be removed, such periodic inspections are conducted at a great expense. However, if service adjustments to the bearings and the lock nuts are not made, serious damage and total failure of major components can result before operators or service personnel even become aware of the problem.
In order to eliminate the need for periodic servicing, numerous means have been devised to maintain the lock nut in fixed position on the shaft so that the bearing will be subjected to a constant preload force. Lock nuts have been employed which include integral synthetic plastic rings and/or plastic washers for securely gripping the coacting threads on the shaft. However, shaft deflection under high loads may cause this type of lock nut to loosen thereby resulting in partial or complete loss of vital bearing preloads.
A key has been utilized between keyways formed in the lock nut and in the shaft to prevent relative rotation of the lock nut. A threaded split nut has also been utilized. These latter two methods do not readily permit small adjustments in the bearing preload. The use of shims in conjunction with a plate fixed to the shaft also has been employed to provide correct positioning of the bearing, but this method does not facilitate quick accurate assembly of the final drive in a production line environment.
A lockwasher which is fixedly secured to the lock nut is available. The lockwasher has internal serrations to prevent rotation of the lockwasher on the shaft and tangs to engage the specially-designed lock nut. Because of the relatively complex cooperating structures necessary to prevent axial disengagement between the lockwasher and the lock nut and the preset tolerance therein, this design is relatively expensive.
It has been found that it is highly desirable to utilize a retainer which can readily be incorporated into existing production designs so as to eliminate any requirement for new machining or assembly procedures.